Apparatus for frequency analysis of atrial fibrillation

ABSTRACT

An apparatus for frequency analysis of atrial fibrillation, as a measure of the state of the illness which includes a device for registration of electrical signals from the heart of a patient, a device for separating a signal originating from the atrium and a device for frequency analysis of the atrial signal. Preferably, the separating device has a system for identification of signals originating from the ventricles, a system for classification of the ventricular signals, a system for formation of the average of the classified ventricular signals and a system for subtracting the averaged, classified ventricular signals from the total registered signal, in order to obtain the atrial signal. Preferably, the registration device comprises electrodes to be placed on the patient and for simultaneous registration of conventional ECG signals.

FIELD OF THE INVENTION

The present invention relates to an apparatus for frequency analysis ofatrial fibrillation, i.e. a means for determining a measure of the stateof illness in connection with atrial fibrillation. The invention may beused to decide if and how the condition is to be treated.

The invention may be regarded as a further development of conventionalECG equipment. By means of the invention, the ECG signals can beprocessed in order to acquire information about the atrial fibrillation.This information will provide useful knowledge about the mechanism ofthe atrial fibrillation and the information will be used for assessingthe state of illness of the patient.

STATE OF THE ART

The electrocardiogram technology (ECG) has been used for a long time tostudy the function of the heart. One disorder of the heart that may bedetermined by ECG is atrial fibrillation. To date, only superficialqualitative analyses of the atrial fibrillation have been performed, andit has not been possible to draw other clinically useful conclusionsthan if it is occurring or not.

With atrial fibrillation, the progression of the illness is sometimessuch that it will reoccur spontaneously after a treatment. With thepreviously known technology it has not been possible to determinewhether the treatment of the atrial fibrillation will be successful orhow long time it will take before the fibrillation will reoccurspontaneously. Consequently, resources have sometimes been usedunnecessarily for ineffective treatments.

The present invention eliminates, or at least reduces, this problemthrough the fact that the atrial fibrillation can be qualitativelyanalysed by studying its frequency behavior. With the aid of theinvention, more accurate predictions can be made about whether atreatment of the atrial fibrillation will be successful or not.

SUMMARY OF THE INVENTION

The invention thus provides an apparatus for frequency analysis ofatrial fibrillation. The apparatus comprises a means for registeringelectrical signals from the heart of a patient, a means for separating asignal originating from the atria and a means for frequency analysis ofthe atrial signal.

Preferably, the registration means comprises electrodes to be placed onthe patient and for simultaneous registration of conventional ECGsignals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail below, with reference to theaccompanying drawings, of which:

FIGS. 1A-D is a diagram showing known different courses of illness inconnection with atrial fibrillation;

FIG. 2A is a schematic illustration of the conventional conductionsystem of the heart;

FIG. 2B shows a normal ECG curve;

FIG. 3A is a schematic illustration of a heart exhibiting known atrialfibrillation;

FIG. 3B is a curve illustrating a conventional electrical signalobtained in connection with known atrial fibrillation;

FIGS. 4A and 4B show various known curves from an ECG registration on apatient with atrial fibrillation;

FIG. 5 is a diagram showing an ECG curve as well as a separated atriumcurve and a separated ventricle curve;

FIG. 6 is a diagram illustrating an example of frequency analysis of theatrium curve of FIG. 5; and

FIG. 7 is a block diagram of apparatus for carrying out the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Investigations have shown that the illness of atrial fibrillation occurswith increasing frequency with increasing age. Below the age of 50 theillness is uncommon, but above that age it increases rather sharply. Itis calculated that in Sweden there are about 100,000 people sufferingfrom this illness in its chronic form.

FIG. 1 shows some typical courses of illness for atrial fibrillation. Inthe diagram, a high level denotes the occurrence of atrial fibrillationand a low level denotes no occurrence. The vertical arrows show wheretreatment has been applied. As shown in curve A, the treatments aretemporarily successful, but the illness reoccurs, each time after ashorter period of time. Finally, it is not worthwhile to perform anytreatment. In the case of B, the illness subsides spontaneously a fewtimes before taking the same course as in A, i.e. finally reaching astate of chronic atrial fibrillation. In the case of C, the illnessoccurs from time to time but never develops into chronic atrialfibrillation. In the case of D, the illness prevails during a prolongedperiod of time but withdraws spontaneously, without treatment. There arethus several varieties in existence and there is a need for an apparatusand a method for evaluating the atrial fibrillation in order todetermine if a treatment has a chance of being successful.

For the sake of easier understanding of the invention, the conductionsystem of the heart will now be briefly explained, with reference toFIG. 2. In the figure, the heart of a patient is shown from the frontside, i.e. to the right hand in the figure is to the left on thepatient, and vice versa. The rhythm of the heart is controlled from thesinoatrial node 1, sending out an electrical signal which is illustratedby approximately concentric, dashed circles. The signals reach theatrio-ventricular node (AV node) 2, acting as a collector and filter forthe impulses from the sinoatrial node. The signals are transferred by a“wire harness” of cardiomuscular fibres 3, to the ventricles. The atriaand the ventricles are otherwise electrically insulated by a barrier 4.

FIG. 2B shows a normal ECG curve. The first pulse P originates from thesinoatrial node, whereas the QRS complex and the T wave emanate from theventricles.

FIG. 3A shows a heart with atrial fibrillation. From the figure it maybe seen that the sinoatrial node cannot perform its function, becausefeedback loops 5 have in some way occurred in the atria and make aconcentric propagation of the sinoatrial node impulses impossible. Afeedback loop may occur around a functional or anatomical obstacle. Atypical feature is the absence of the so called P wave in the ECG.

FIG. 3B shows a typical signal from a heart with atrial fibrillation.The signal consists of a fibrillation signal superimposed on theventricular signal, of which the peaks R are easily identifiable.

The following applies:

WL≧CV×RP

where WL is the wave length (˜1/f), CV is the conduction velocity and RPis the refractory period, i.e. the recovery period of the cardiomuscularfibre after excitation by an electrical pulse. It has been found thatthe shorter the wave length, that is, the higher the frequency, the moredifficult it is to treat a heart for fibrillation. Consequently, it isof interest to study the frequency of the atrial fibrillation, which thepresent inventor have realized.

In FIGS. 4A and 4B, a registration is shown of an ECG on a patient withatrial fibrillation. The various signals V1-V6, AVL, I, -aVR, II, aVF,III are those normally registered during an ECG by surface electrodesapplied to the body of the patient at conventional locations. If theheart had been healthy, a P wave could have been observed, which wouldhave been most clearly visible in the signals V1 and II. Now, there isinstead a superimposed fibrillation signal occurring.

In FIG. 5 is shown how, with the aid of the present invention, thefibrillation signal or atrial signal is extracted. The unprocessed ECGsignal V1 is shown at the top of the figure. A conventional ECGequipment is supplemented with various devices for processing the ECGsignal. First, the easily identifiable QRS peaks are identified. The QRSpeaks are then individually classified into various types. Subsequently,a time average over the registration period is formed within each type.The averages of the classes are then subtracted from the total ECGsignal, whereby the pure fibrillation signal subecg is obtained. Thediagram also shows the signal syntecg which has been calculated andwhich is subtracted from the total signal. This signal corresponds tothe “ventricular signal”.

The fibrillation signal obtained can be analysed subsequently with afrequency analyzer. FIG. 6 shows a diagram of such an analysis. As canbe seen, the fibrillation has a frequency peak at about 7 Hz, whichcorresponds to a cycle length C1 of about 145 ms and 420 beats perminute (BPM). A lower value of the cycle length (or a higher frequency)for the location of the peak in the frequency analysis corresponds to ahigher tendency towards arrhythmia. It may also be of interest to studythe distribution of the pulse frequency, e.g. the pulse width at a givenlevel.

This type of signal processing can also be performed on signalsregistered in the esophagus, or from the inside of the heart via cardiaccatheters.

As a complement to the surface electrodes of the ECG equipment,oesophagal electrodes may be used. Such electrodes are swallowed by thepatient, into the esophagus, and are positioned close to the heart. Itis possible to come especially close to the atrium and the ventricle onthe left side. With the aid of the esophagal electrodes, signals from amore delimited part of the heart may be selected. This may be of useduring a study of the origin and the mechanism of the fibrillation.

The present invention thus provides a further development of the ECGtechnique for qualitative studies of especially atrial fibrillation. Themajor advantage over conventional ECG is that it enables an assessmentof whether resources should be used, in the form of time, medicine andelectrical treatment, or a patient with atrial fibrillation. The variousmeans for registration of the electrical signals and for processingthem, in the way prescribed by the invention, are based on conventionaltechnology and do not present any design problems to a person skilled inthe art. Machinery and software for frequency analysis and signalseparation are commercially available. The scope of the invention isonly limited by the accompanying claims.

What is claimed is:
 1. Apparatus for frequency analysis of atrialfibrillation, characterized by a means for registration of electricalsignals from the heart of a patient; a means for separating a signaloriginating from the atria from the registered electrical signals; and ameans for frequency analysis of the atrial signal.
 2. Apparatusaccording to claim 1, characterized in that the separating meanscomprises devices for identification of signals originating from theventricles, devices for classification of the ventricular signals,devices for formation of the average of the classified ventricularsignals and devices for subtracting said averaged, classifiedventricular signals from the total registered signal, in order to obtainthe atrial signal.
 3. Apparatus according to claim 1, characterized inthat the registration means comprises surface electrodes to be placed onthe patient.
 4. Apparatus according to claim 3, characterized in thatthe registration means comprises surface electrodes for ECGregistration.
 5. Apparatus according to claim 3, characterized in thatthe registration means comprises electrodes for location inside theesophagus of the patient, for selective registration of signals. 6.Apparatus according to claim 2, characterized in that the registrationmeans comprises electrodes for location inside the heart of the patientvia cardiac catheters, for selective registration of signals. 7.Apparatus according to claim 1 or 2, characterized in that the frequencyanalysis means comprises devices for the calculation and display of themean frequency of the atrial fibrillation and a distribution value.